A gas turbine engine typically includes a fan section, a compressor section, a combustor section, and a turbine section. Air entering the compressor section is compressed and delivered into the combustion section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section.
In the pursuit of ever high efficiencies, gas turbine engine manufacturers have long relied on high turbine inlet temperatures to provide boosts to overall engine performance. In typical modem gas turbine engine applications, the gas path temperatures within the turbine section exceed the melting point of the component constituted materials. In order to operate the gas turbine engine at these temperatures, dedicated cooling air is extracted from the compressor section and used to cool the gas path components in the turbine section. The use of compressed air from the compressor section for cooling purposes decreases the efficiency of the gas turbine engine because the compressor section must produce more compressed air than is necessary for combustion. Therefore, minimizing the use of cooling air in the turbine section is of particular importance.
Typically, the leading edge region of a turbine airfoil experiences the highest heat load of the entire airfoil. The heat transfer coefficients located at the stagnation point of the airfoil are typically 1.5-2 times the values seen on the downstream portions of the airfoil. Due to the elevated heat loading at the stagnation point, airfoil cooling configurations are typically setup to produce the highest cooling effectiveness in this location, which in turn consumes one of the largest amounts of compressed air from the compressor section.
Turbine airfoil leading edge cooling configurations which utilize a highly convective impingement cavity feeding multiple rows of film holes can incur a relatively high pressure drop across the impingement holes. This pressure drop can lead to conditions where the circuit cannot positively purge the film holes leading to hot gas ingestion. As a result, compromises in back-side cooling effectiveness are made to mitigate this loss in pressure, such as over-sizing the impingement holes which decrease the impingement jet velocity and the overall impingement heat transfer efficiency. Thus, new and improved cooling configurations for airfoils which allow for significant heat transfer coefficient production while minimizing prohibitive pressure losses are desired in the art.